Technical Field
The present disclosure relates to Nano-Composite Materials (NCMs), and methods of making or functionalizing the same. Specifically, the NCMs may include multiple types of nanoparticles combined together into a single composite material or the NCM may be a combination of nanoparticles and macro-scale substrates.
Description of the Related Art
Many nano-materials, including carbon nanotubes, graphene, buckyballs, carbyne, nano-diamonds, nanoparticles of titanium dioxide, silica, tungsten, magnetite, and other metal, semiconductor, and metal oxide nanoparticles, exhibit exceptional mechanical, thermal, optical, catalytic, magnetic, and/or electrical properties. Compositing two or more nanomaterials could potentially improve electrical, thermal, optical, mechanical, or chemical interfaces between said nanomaterials.
Numerous methods have been developed to attach, or “functionalize,” specific chemical or functional groups to target materials, including nano-materials and macro-scale material surfaces. These chemical groups can then further bond or adsorb to additional chemicals, other nanoparticles, or provide anchors for attachment to macro scale surfaces in the form of self-assembled monolayers (SAMs) or self-assembled poly-layers (SAPs). In general, material-specific functionalization protocols are designed and employed in order to ensure the specificity or selectivity for attaching the chemical groups.
On the other hand, a few processes, including those that use thiols or reactive diazonium salts, can be widely applied to functionalizing materials such as all forms of carbon, numerous metals, and semiconductors.
For example, a common, material-specific functionalization process for graphitic carbon materials, such as carbon nanotubes, graphene, or buckyballs, employs strong oxidizing agents, such as a mixture of concentrated sulfuric acid and nitric acid. In addition, the process requires harsh sonication treatments that introduce defects onto the otherwise stable, relatively inert graphitic structure. The combination of oxidation and sonication is capable of forming a non-stoichiometric number of mixed chemical groups, such as hydroxyls, carboxyls, ketones, etc. Some of these chemical groups can then be used as anchors for further attachment of functional groups, to enhance solubility in certain solvents, or for other application-specific purposes.
Another example of functionalization is more general in its range of target materials and also more precise in its ability to stoichiometrically functionalize a substrate. The process involves treating a target material with an aryl diazonium salt, such as 4-carboxybenzenediazonium tetrafluoroborate, under conditions that facilitate electron transfer to the diazonium salt, thereby generating a transient aryl radical. The transient and reactive aryl radical then forms a carbon-substrate bond with the substrate. The reaction conditions required for diazonium functionalization are relatively mild, as are the facile formation of a direct carbon-substrate bond. Thus, diazonium functionalization is widely used for many materials, including silicon; gallium arsenide; copper; gold; palladium; zinc; zinc oxides; titanium; tungsten; ruthenium; platinum; iron; iron oxides; copper oxides; tungsten oxides; all carbon allotropes that have either graphitic structure, alkene or alkyne functional groups, or molecular defects; and many more nano-materials and substrates.
In fact, due to the broad range of substrates and the ability to form extremely strong carbon-substrate bonds with many materials, including carbon itself, diazonium functionalization is considered one of the more important reactions in nanomaterial science. However, because the diazonium functional group is so unstable that only aryl compounds will not spontaneously decompose, the molecules used to functionalize materials using diazonium are limited to functionalities which have an aryl ring between the functionalized nanomaterial or substrate and the desired functional groups attached. This limitation can often reduce atom efficiency, limit material properties, or prevent the use of less expensive precursors for a specific functionalization task. Accordingly, there is a need for a process that could functionalize a nanomaterial or macro-scale material surface by more versatile attachments and functional groups.